Insulating and sealing means for electric discharge devices



se m, 1936. WAMLKIN 2,053,122v

INSULATING AND SEALING MEANS FOR ELECTRIC DISCHARGE DEVICES Filed Jan. 22, 1952 I Inventor:

William Awu ins,

by His Attorney.

Patented Sept. 1, 1936 UNlTED STATES PATENT OFFICE INSULATING AND SEALING MEAN S FOR ELECTRIC DISCHARGE DEVICES New York Application January 22, 1932, Serial No. 588,150

3 Claims.

My invention relates to means for and methods of insulating the electrodes of electric discharge devices, particularly the mercury cathodes of mercury arc rectifiers or inverters, from the 5 metallic evacuated receptacles of such devices, and has for its object the provision of improved insulating means and methods for this purpose.

In the operation of mercury arc rectifiers and similar discharge devices having a liquid cathode contained in the lower portion of a metallic evacuated receptacle or tank it is necessary that the liquid cathode be insulated from the tank. Further, since the tank cannot, therefore, be utilized as a circuit member to conduct current from the 15 mercury cathode, other conductive members must be provided for the latter purpose and such members must be insulatingly sealed from the metal tank.

It is customary to meet the above-noted re- 20 quirements by providing a mercury cathode receptacle of conductive or other material separate from and below the evacuated receptacle or tank and insulated therefrom, if formed of conductive material, by suitable rings of insulating material 25 compressed between the cathode receptacle and the tank. I have found however that in certain cases the above-described construction comprising a relatively bulky and costly mercury cathode container separate from the tank may be dis- 0 pensed with to advantage by means of a novel construction associated with the lower portion of the rectifier receptacle or tank.

In accordance with my invention the usual mercury cathode insulating means is replaced by a 35 thin coating or layer of similar refractory mateas a coating of enamel, extending over the inner surface of the lower portion of the tank, and a thin coating or layer of similar refractory material interposed between a pair of sealing surfaces 40 formed respectively on the lower wall of the tank and on a metallic member which is in electrical contact with the liquid mercury of the cathode. The sealing surfaces are spaced apart a suitable small distance by granules of refractory material 45 contained in the enamel coating.

My invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

50 Referring to the drawing, the single figure thereof is a side elevational view partially in section of an electric discharge device in which my invention has been embodied.

The electric discharge device shown in the fig- 5 me for the purpose of illustrating the invention is a mercury arc rectifier or inverter comprising a metallic evacuated receptacle or tank I in the lower portion of which is a liquid or mercury pool cathode 2. In accordance with my invention, in order to insulate the current conductive element 5 or mercury pool 2 from the walls of the tank I a thin coating of refractory material or enamel 3 is baked directly upon the inner wall of the tank, this coating preferably extending upwardly from the surface of the mercury pool a substantial distance.

Further in accordance with my invention, in order to provide means to conduct current from the cathode 2 to an outside circuit (not shown), a conductive element, such as a cup-shaped or urnshaped metallic member 4, is provided having a sealing surface 5 arranged to be fitted in close proximity to a corresponding sealing surface 6 formed on a downwardly extending portion 1 of the evacuated tank I. To insulate the metallic conductive element or cup 4 from the tank portion 1 an enamel coating 8 containing grains of sand for properly spacing the cooperating sealing surfaces is baked to these surfaces, thereby forming an insulating and vacuum tight seal therebetween.

I have found that the member 4 and the tank portion 1 should be formed with upwardly and outwardly extending fiange portions on which the surfaces 5 and 6 are spun, in order to prevent the enamel 8 from overbaking.

Preferably the enamel coating 3 extends over the entire inner surface of the rectifier tank 1 below the equator, or central horizontal plane, and also downwardly over the inside surface of conductive member 4 to a point thereof substantially below the sealing surfaces 5, 6. The mercury pool 2 is therefore effectually prevented from coming into contact with any metal surface except that surface of the conductive element 4 which is at the lower end thereof.

The vitreous enamel forming the insulating and sealing material as above described contains preferably a large percentage of glass, the other ingredients being borates, clay, and magnesium carbonate. This mixture provides a satisfactory coating for the metal surfaces upon which it is baked since the mixture has substantially the same coefiicient of expansion as the steel of which the Walls of tank I and conductive member 4 are composed.

Instead of employing sand grains as spacing material between the surfaces 5, 6 grains of other insulating materials, such as magnesium oxide, fired talc, porcelain, quartz, alundum or similar materials, may be employed. The seal between the surfaces 5, 6 is so formed that these surfaces are spaced apart to 6 by therefractory sealing material.

In the foregoing description of one embodiment of my invention I have illustrated the insulating and sealing means as employed for the purpose of bringing out a current conducting lead, as conductive element 1, from the liquid cathode 2 of an electric discharge device. It will be readily understood however that the sealing means herein described, comprising a thin enamel coating baked upon sealing surfaces spaced apart a short distance by refractory material included in the enamel layer, may be applied equally well to bring out the current leads of other electrodes of a mercury arc rectifier or other electric discharge device.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric discharge device, an evacuated metallic receptacle, a liquid electrode in said receptacle, that portion of said receptacle which contains said liquid electrode having an the lower portion of said receptacle, a coating of refractory material on the inner walls of said lower portion of said receptacle to insulate said electrode from said walls, a hollow metallic extension of said lower portion of said receptacle having therein a portion of said liquid electrode to conduct current from said electrode, said lower portion of said receptacle and said extension having sealing surfaces spaced closely adjacent each other, and refractory material interposed between and baked on said surfaces to maintain insulatingly said spaced surfaces in vacuum tight relation, said last-named refractory material constituting the sole means for supporting said metallic extension in operative position relative to the sealing surface of said receptacle.

3. In a vapor electric device, an evacuated metallic receptacle, a liquid electrode contained in the lower portion of said receptacle, said lower portion being coated with a refractory material to insulate said electrode from said receptacle, and a hollow metallic member in contact at the lower inner Wall with said liquid electrode to conduct current therefrom; said lower portion of said receptacle and said metallic conducting member having sealing surfaces spaced closely adjacent each other, said surfaces being coated with a refractory material to form a vacuum tight seal between said surfaces and to insulate said metallic conducting member from said receptacle, said last-named coating constituting the sole means for supporting said metallic member in operative position relative to the sealing surface of said receptacle.

. WILLIAM A. WILKINS. 

